#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include<math.h>
int main()
{
	float x1 = 0, y1 = 0, x2 = 0, y2 = 0;

	while (scanf("%f %f %f %f", &x1, &y1, &x2, &y2) != EOF)
	{
		float ret = sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2));
		printf("%.2f\n", ret);
	}

	return 0;
}